1. Field of the Invention
The present invention relates in general to compounds for use in electrochromic (EC) devices and, more particularly, to anodic compounds including substituted 5,10-dihydrophenazine compounds and associated derivatives thereof which are useful in solution phase EC devices.
2. Background Art
Variable transmittance light filters, such as electrochromic light filters, have been proposed for use in architectural windows and skylights, as well as in windows and sunroofs for automobiles—just to name a few. Such electrochromic light filters reduce the transmittance of direct or reflected sunlight during daytime through the window, while not reducing such transmittance during nighttime. Not only do the above-identified electrochromic light filters reduce bothersome glare and ambient brightness, but they also reduce fading of interior materials and heat load caused by the transmittance of sunlight through a window. In addition, electrochromic mirrors have become popular in the automotive industry for reducing glare from the headlamps of following cars during nighttime driving.
Solution phase electrochromic devices are well known in the art. See, for example, U.S. Pat. No. 4,902,108 entitled “SINGLE-COMPARTMENT, SELF-ERASING, SOLUTION-PHASE ELECTROCHROMIC DEVICES, SOLUTIONS FOR USE THEREIN, AND USES THEREOF,” which is hereby incorporated herein by reference in its entirety—including the references cited therein. In solution phase electrochromic devices, 5,10-dimethyl-5,10-dihydrophenazine (sometimes referred to herein as “DMP”) is commonly used as an anodic material. The use of DMP (a good electron donor/anodic material) in a solvent with a 4,4′-bipyridinium compound (a viologen), such as 1,1′-dioctyl-4,4′-bipyridinium bis(tetrafluoroborate) (a good electron acceptor/cathodic material), leads to the formation of a charge transfer band that exhibits a broad absorbance near 800 nanometers (nm). Preferably, the presence of such a charge transfer complex, and associated absorbance, would be eliminated or at least substantially reduced for numerous performance and/or stability reasons. Other anodic materials have been discussed in the art. See, for example, U.S. Pat. No. 6,020,987 entitled “ELECTROCHROMIC MEDIUM CAPABLE OF PRODUCING A PRE-SELECTED COLOR,” which is hereby incorporated herein by reference in its entirety—including the references cited therein. While the '987 patent discloses compounds which exhibit reduced charge transfer band absorbance with a viologen in solution, such as 5,10-diisopropyl-5,10-dihydrophenazine, to the best of Applicant's knowledge none of the compounds disclosed in the '987 patent have replaced DMP as the preferred anodic compound for use in solution phase electrochromic devices.